Insulating materials resistant to attack by molten metals, including aluminum alloys, are known to the prior art. For example, Moritz U.S. Pat. No. 3,212,142 discloses a process and apparatus for continuous aluminum casting. The apparatus includes a mold having an outer metal shell lined with an annular header or liner of insulating material. The insulating header is made from a composition wherein asbestos fibers are distributed in an inorganic binder.
Asbestos-containing insulating materials have performed satisfactorily in the aluminum industry for several years. However, it is now necessary to discontinue usage of asbestos-containing materials because of health concerns. Accordingly, there is presently a need for asbestos-free insulating materials suitable for use as headers in continuous aluminum alloy casting.
Barrable U.S. Pat. No. 4,101,335 claims a fire-resistant asbestos-free building board comprising mica or a mixture of mica and standard vermiculite distributed in a calcium silicate binder. Barrable U.S. Pat. No. 4,132,555 claims an asbestos-free building board comprising standard vermiculite distributed in a water-soluble binder containing organic reinforcing fibers. Neither of the Barrable patents suggests utilization of delaminated vermiculite or spodumene or lithium aluminate as an asbestos substitute.
A principal objective of the present invention is to provide an insulating material suitable for use as a header in continuous molten metal casting.
It is a related objective of the invention to provide an insulating material of the type described wherein asbestos is replaced by delaminated vermiculite, spodumene, lithium aluminate, or mixtures thereof.
Another objective of the invention is to provide an insulating material that is resistant to attack by molten metal, demonstrates low absorption of oils used as parting compositions, and has satisfactory strength.
Additional objectives and advantages of the invention will become readily apparent to persons skilled in the art from the following detailed description of our invention.